Electron discharge device and associated circuit



May 8, 1951 2,552,334

ELECTRON DISCHARGE DEVICE AND ASSOCIATED CIRCUIT E. e. LINDER 2 Sheets-Sheet 1 Filed March 2, 1945 m m w m ERNEST E. LINDER BY .%WW

y 8, 1951 E. G. LINDER 2,552,334

ELECTRON DISCHARGE DEVICE AND ASSOCIATED CIRCUIT Filed March 2, 1945 2 Sheets-Sheet 2 INVETOR. EST El. LINDER 82 ERN rroemy Patented I May 8, 1951 "ELECTRO D S'GHARGE newer;

ASSOCIATED CIRCUIT Ernest G. Linder, Princeton, N. -J., assig'nor to Radio Corporation of iflmerica, a corporation of Dela-Ware Aisliiicationmarhz, 1945,SeriaiPNofi580509 My inventionrelates' to electron discharge devices and associa'tedcircuits, more' particiilarl'y to such devices using cavity resonators.

In one form of ultrahigh frequency ap'pa -"altu's, an electron discharge "device is associated with-a cavity resonator'cir'cuit in such a manner that an electron beam is directed through the' resonator either forcontrol purposes er for the purpose of extracting energy from the electron stream by the resonator. "Thisa'iiip'aratiismay include a resonator having oppositely disposed apertures in the walls of the resonator and through which an elongated electron discharge device extends so that the cathode is positionedon' one side of the resonator with the collector or reflector on the other side of the resonator. Various arrangements'have been utilized.

As the frequencies 'at which th'e apparatus is operated are increased, the dimens'iohS of both the resonator and the electr'on discharge device must be decreased with the result that the electrode structures become increasingly sm'alle'r, limiting the power 'output of the apparatus 'aiid the ability to dissipate heat. Small electrode structures introduce manufacturing 'tiifiiculties and to i-nsur-e that *the tran'sit 'tiirle bi the electrons through the resonator-tails withinthelim its required for operation' aft thse high frdiin cies, it is necessary to usel-ii'gh accelerating volta'gesbetween the various-electrodes. I-n o'rder' to limit the transit time- 6f the electrons tlirou'g' h the resonator, the portion of the resonator across which the beam --is-'- directed became increasingly constricted, thus introducing structural di fiiculties in the manufactureof the resoiiator.

It is, therefore,-an object-of my invention to provide an electron discharge device and as; sociated 'circuit of the cavity resonator typeof improved design.

A furtherobject of "my invention isto'provide an electron dischar'gedevice and'as's'ociated ca'vit'y resonator circuit which is useful at very jlii'gh frequencies and yet in which a comparatively large electron discharge'devicemay be usedQt hus A further object of my invention -is to pi ovi'de such-an electron discharge device and associated :2 cavity resonator whichcanbe made of reasonable size, facilitating assembling andha'ndlin'g.

A more specific "object of my invention is to provide 'such an 'eleetron discharge device and associated cavity resonator in which thecon'- strictedipor'tion through which the beam of electrons :p'asses is not a Jimiting -factor on the size of the resonato'r but which nevertheless permits the use oi 'alarge size cavity resonator which may be operated a't' very hi'gh 'frequencies.

The riovel features which :I believe to be characteristic of my inventionare set forth with pa'rticularity in the appended' claims, blltthBfiIWEntion itself -will best Hoe understood by referen'ce to the following description taken in connection with the accompanying drawing in which Figures'1 and2 are pers'pecti'vevie'ws of cavity i es'o nator's illustrating the principle of' my invention, Figure 3 is an electron discharge d'evice and associated cavity re'sona'tor circuit m'ade acco'rd ing to my 'invention, Figiire '4 is an rilar'gedfilab tioii taken along 'the 1inefiv lv of F iglil e 3-aiifl showing-details of construction, =F-igi-i1-e 5 is a perspective of a 'inodifiedform of electron discharge device an d associated circuit in-ade accorliiri'g to my: invention, Figure 6 is a side elevation of the apparatus shown: in Figure-5 wi th pai' ts in section 111g details of construction, :Figures 7 and e 21 681111 aiid'lside elevations"withipafits in section of a' 'mddifi'ed i form of an electron discharge de- Vi'Ge aIn'd associated cavity rson aitor-eirbuit iriade according t'o -in-"y i'nyentio'n, f9 is a'tran's verse section-6f a s'till furtlier niodification of an electron discliar'ge 'dvice ain'd associated caii'i-ty resonator circuit made a cordin to I my invention, and Figures 10 and -11 show fiirthr f6 ms of an electron dischar 'g'e device and assoc'atea cavity resonators made according to iny invention.

-It is Known that' in the c'ase'ef waveguides wavelength'of the propaigated{wave therihi eqiie'ritly independent of -one 6f the difiiension of the waveguide. Referring to 'F-igur'e 1 for' ample, there is shown a rectangular giiiie-h'av i'rig dimensions a, b and length- L. Wlieh an Hn;1 wave with the electric field parallel to the dimension n along the r'ri-in'or transverse or the '{giii'cle is transmitted through {the waveguide from one "end to the other along t'he dim'risidn L it has been found that the-" iliinei-ision a may be varied without "a'ifti'rig the wavelength in the guide. The s'ai'ne -holds"' true 'for 1 10.2 wave. and also for higher orders.

armcieiemaybe arafili'ed "to "closedc'avity resonators "which "may b'e regarded ats resonant sections of waveguides. For example, if the resonator of Figure 1 is a resonant section a wavelength long, we have where A is the wavelength in the resonator and \e is the length of the wave in free space. It can be seen that the resonator wavelength is independent of the dimension 0.. Hence a may be varied at will to suit any special purpose.

A form of resonator particularly and peculiarly suitable for use in combination with an electron discharge device to provide a high frequency apparatus useful as an oscillator or as an amplifier is shown in Figure 2. Here the dimension, a is made much smaller at one end 22 than at the other end 2|, and calculations for wavelength by the above formula and wavelength measurements on actual construction show a very close agreement with each other. The Q of the resonator is very high. Preferably, the two resonator portions 21 and 22 are connected by a tapered transition portion 23 integral therewith, as shown, to avoid refiections in the resonator due to abrupt discontinuities in the walls thereof.

Apparatus made according to my invention is illustrated in Figures 3 and 4. In this arrangement an elongated electron discharge device or tube, having an envelope 25, an indirectly heated cathode 26 at one end, a collector or refiector 21 at the other end and intermediate grids 28 and 29 having grid contact and supporting rings 28' and 29 sealed through envelope 25, is used in combination with a cavity resonator 30 of the form shown in Figure 2. The lower end portion 32 of the resonator is a section of constricted transverse dimension in the direction of the path of the electron beam and the resonator is enlarged at the other end portion 3!. The overall length of the resonator is preferably about one wavelength in the resonator, as in Figs 1 and 2, so that standing wave will be set up therein in the second harmonic mode of operation, considering the fundamental as the first harmonic. For optimum results, the beam should pass through the resonator at a voltage maximum of the standing-Wave pattern therein. Hence, the discharge device is located along the resonator 30 at a distance of approximately a quarterwavelength in the resonator from the closed end of the constricted portion 32. The lower end portion 32 is provided with a pair of oppositely disposed apertures 33 and 33 through which the electron discharge device extends. The contact and supporting rings 28' and 29' provide electrical connection between the grids and inwardly-extending spring finger contacts such as 35 on a ring 34 mounted on the resonator walls. Thus the grids in effect form continuations of the resonator walls, providing a foraminous portion through which the electrons may be directed.

Since the size of the opening is not restricted in any Way by the constricted portion of the resonator, large electrodes can be utilized and since the width of the resonator in the direction of the path of the electron beam can be made of any desired value, the'transit time of the electrons through the resonator maybe small even with very low voltages atvery high frequencies.

A further advantage of the type of resonator utilized in Figure 3, of importance especially with 4 very short waves, such as from 5 centimeters to .5 centimeter, is that this type of cavity resonator may be used as a wave magnifier. This is evident from the formula By varying the dimension D the cavity resonator wavelength may be changed all the way from A8 to infinity, the latter value being attained when b is equal to This is several times larger than, for example, a toroidal resonator of the same length would be and permits the use of considerably more beam current.

High frequency energy may be introduced into the cavity resonator 30, or extracted therefrom, by any conventional means, such as a coupling loop 36, linked with the transverse magnetic component of the electromagnetic field within the resonator, forming a continuation of the central conductor of a coaxial transmission line 37, 38, as shown in Fig. 3. 7

In the modification shown in Figures 5 and 6, the electron discharge device is provided with an envelope 40 having at one end an indirectly heated cathode M and at the other a collector 42, a plurality of contact ring type grids 43 being spaced along the length of the tube. These grids may be of the form shown in Figures 3 and 4.

The cavity resonator 44 utilized in this arrangement is provided at its lower end with a plurality of restricted cavity resonator portions 45 instead of one as shown in Figure 3. The electric fields at any instant within the several restricted portions 45 will lie in the same direction parallel to the electron path. If the successive grids are equally spaced and the transit time of the electrons therethrough be suitably adjusted, each electron will be continuously accelerated or decelerated,, depending on the time of entry into the resonator. This type of tube can be used for various purposes and it is of course understood that the transverse dimensions through the constricted portions 45 will be that required depending upon the use to which the apparatus is to be put. For example, if energy is to be extracted from the beam, the spacing between successive pairs of grids will be shorter as the electrons slow down, if operation requires this arrangement. On the other hand, if electrons are continuously accelerated then the spacing between the successive grids will be in- 1.8 centimeters creased to' take caremrniisprcvisicn. Thedaif a low positive or-hegati-ve' voltagewereapplied to "the electrode 42 fordirecting electron groups backthrough the last of the constricted portions 45. Various other modifications readily suggest themselves.

In Figures 7 and 8' a still further modification ofan apparatus made according to my inven tion is shown. In this arrangement -I provide the"e'lectron discharge device with an envelope 50 in which is mounted an indirectly heated cylindrical cathode surrounded bya tubular control electrode EZ'having foraminous portions 53 through which the electrons are directed in oppositely disposed beams. This "electrode 3'22 may "be capacity coupled to the resonator 54, or directly connected thereto at the ends as shown in Fig. 8, depending upon whether or not it is "desired to apply "an alternating control voltage to the 'electr'ode 5 2. The resonator =54 in the form of a flat rectangular shaped resonator maybe 'closed'at oneend 55 andopen at'its other end 56 and provided intermediate its ends with "foraminous portions 54 through which the electrons "are directed toward "two "electrodes 5'1, which'may be used "as collectors or as reflectors,

these electrodes being ,providedwith leads ti.

The "open end '56 "(if the "resonator "within the envelope '50 communicates with the interior of the enlargedportion of the resonator Edthioiigh neckta, which telescopes over the envelope "and the open end of the resonator.

The cathode '5] is supported at its opposite ends from the resonator '5 within the envelope by means of insulating discs "51"., preferably of mica, and is provided with a pair of heater leads 6]], one of which may be connected to thecathode to provide the cathode lead. The resonator may be provided with a lead 54' upon which a high potential may be applied for biasing purposes with respect to the cathode and to which may also be applied an alternating voltage for modulating or controlling the passage of -electrons through the resonator. The portion 58 of the resonator external of the envelope need not have any voltage applied thereto, thereby providing a safety feature.

Electrons may be accelerated :andcontrolled :in the'space between the electrode 52 and cathode 5| and passed through the space between the foraminous sections of the resonator, either to excite the resonatoror be reflected back through the resonator by electrodes 51 so that the whole apparatus functions as an oscillator.

Figure 9 shows a transverse section .of another form of my invention in which the electron discharge device is provided with an envelope 65 and in which are mounted an indirectly :heate'd cathode 66 and an oppositely disposedcollectorzor reflector 6-7, electrons from the cathode to the collector passing through'an'arcuate shapedc'dnstricted resonator 68 at foraminous portions 69 and H3. The open end 68' ofthereSona'tor' BB communicates with the interior of an enlarged resonator H in the manner shown inFig'ure's '7 and 8.

:Another f orm of multiple action apparatus is shown in Figure 10 and-a turther modification in Figure 11, in which the constricted portion of th'e resonator through'which tube '15 extends isfolded. In the arrangement shown in Figure l0,-"the distance'bei'iw'een folds 1"! is preferably equal to the thickness of the cavity and hence 6 the electrons travelling with constant velo'c'ity' through the "grids or iape-rtures' will spend-equal time inside and outside the' iolds. of each ram is -equa1 to 7 hence the electric fields at any instant inside all the folds at the apertures will lie the same direction parauel to the electron path, and the field's between the folds will lie in the opposite direction. By adjusting 'the-speedof the electrons,3altei'nate-ha1f periods will he spent inside the resonator-and' the field seenby-ea'chelectron will always be in the same-direction so thatelectrons would always be accelerated -or decelerated, depending upon the time of entry of the electrons into the initial portion 16*of the resonator. The enlarged portion-of the resonator communicates with the restricted portion as shown.

--A similar effect would be obtained *by the arrangement show-n in Figure 11. Folding is again -employ'ed here but the folds are in "contact with each other so *tha't'only the thickness of the *metal separates adjacent interior "sections. In this case the cavity resonator is op-'- quencethe field in the "entire folded section'is in "the same phase. However, adjacent sections will have reversed field directions at any instant due to folding. Thus electrons travelling at such speed as to require a half period "to"'pa"s's through each fold will be "continuously "accelerated "or decelerated. This applies to devices employing small degrees of "oscillation, Such as detectors and converters. v

'It is of course obvious that "the resonators could be used 'as part of "the tube envelope.

While I have indicated the preferred embodiments'of my invention'of which I am now aware and have also indicated only one specific application for whichmyinventi'on may be employed, it will be apparent thatmy 'invention'is by no means limited to the'ex'act form's illustrated or the use indicated, "but that many Variations be made in the particular structure used and the purpose io'r'whic'h it is employed without-departing from the scope "of my invention as set forth in the appended claims.

-What I claim as new 1. An electron discharge device having a cathode for supplying "a stream of electrons along a given path, an electrode spaced from said cathode -and*positioned in said 'path toward'wliich electrons are directed during operation of said device, and an elongated cavity resonator closed at both ends and having 'a predetermined resonant "frequency and positioned between said cathode and said electrode and through which said "electron path 'lies, said cavity resonator comprising an elongated hollow conducting member of substantially uniform transverse dimension therethrough normal '"to said path'and haping an overall length of approximately one wavelength in the resonator of the operating frequency of "saiddevice and having at one end thereof a section of constricted transverse dimension normal to said uniform transverse "dimens'ion, said electron path extending through said section in a direction "parallel to said constricted transverse dimension.

2. An electron discharge device having 'a cathode forsupplyin'g a stream of electrons along a given path and an "electrode in Said path "to- The length ward whichsaid electrons are directed during operation of said device, and an elongated cavity resonator closed at both ends and having a predetermined resonant frequency and positioned between said cathode and said electrode and through which said path lies, the longitudinal axis of said resonator being normal to the path of the electron stream, said resonator being of substantially uniform transverse dimension normal to said electron path and having two communicating portions of substantially difierent transverse dimension parallel to said electron path, the electron path passing through the portion of smaller transverse dimension.

3. An electron discharge device according to claim 2, wherein said two communicating resonator portions are connected by a tapered portion integral therewith.

4. An electron discharge device having a cathode for supplying a stream of electrons along a given path, an electrode in said path spaced from said cathode and toward which said electrons are directed during operation of said device, and an elongated cavity resonator positioned between said cathode and said electrode and through which said path lies, said resonator having an overall length of approximately one wavelength in the resonator of the operating frequency of said device and comprising two communicating portions of substantially different transverse dimension parallel to said path, said passing through the portion of smaller transverse dimension.

5. An electron discharge device according to claim 4, wherein said two communicating portions are connected by a tapered portion integral therewith.

6. An electron discharge device having a cathode for supplying a stream of electrons along a given path and an electrode in said path spaced from said cathode and towards which said electrons are directed during operation of said device, and an elongated cavity resonator closed at both ends and having a predetermined resonant frequency and positioned between said cathode and said electrode and through which said path lies, said resonator comprising a first portion of given transverse dimension in one direction, a second portion of substantially greater uniform transverse dimension in said direction and a third portion whose transverse dimensions in said direction at the ends thereof are equal to said first and second portions, respectively, connected between said portions, said first portion having apertures in opposite walls thereof through which said path extends in said direction.

7. A cavity resonator of predetermined resonant frequency for use with a high frequency electron discharge device, comprising an elongated hollow conducting member of substantially uniform transverse dimension in one direction, said member being closed at both ends and having two communicating portions of substantially diiferent transverse dimension normal to said uniform transverse direction, opposite walls of the portion of smaller transverse dimension being apertured to permit passage of an electron beam therethrough.

8. A cavity resonator of predetermined resonant frequency for use with a high frequency electron discharge device, comprising an elongated hollow conducting member closed at both ends and having at one end a plurality of parallel portions of restricted transverse dimension, the

8. walls of said restricted portions being provided with registering apertures to permit passage of an electron beam therethrough.

9. A cavity resonator of predetermined reso- 1 nant frequency for use with a high frequency electron discharge device, comprising an elongated hollow conducting member closed at both ends and having a folded portion of restricted transverse dimension, the Walls of said folded portion being provided with registering apertures to permit passage of an electron beam therethrough.

10. A cavity resonator according to claim 7, wherein the transverse section of said elongated hollow conducting member throughout the length thereof is rectangular in form with said uniform transverse dimension lying parallel to the major axis of the rectangle.

11. A cavity resonator according to claim 7, wherein the overall length of the resonator is approximately one wave-length in the resonator of the operating frequency thereof.

12. A cavity resonator of predetermined resonant frequency for use with a high frequency electron discharge device comprising an elongated hollow conducting member closed at both ends and having a first portion of given uniform cathode for supplying electrons along a given path, and an electrode in said path toward which said electrons are directed during operation of said device, and an elongated cavity resonator closed at both ends and having a predetermined resonant frequency and positioned between said cathode and said electrode and through which said path lies, the longitudinal axis of said resonator being normal to said path, said resonator having rectangular transverse cross sections at different positions along the length thereof parallel to said electron path, the transverse cross section of the portion of said resonator through which said electron path lies having a dimension parallel to said electron path smaller than the corresponding dimension of other portions of said resonator.

14. An electron discharge device having a cathode for supplying electrons along a given path and an electrode in said path toward which said electrons are directed during operation of said device, a pair of spaced electrodes positioned between said cathode and said electrode in said path, and an elongated cavity resonator closed at both ends and having a predetermined resonant frequency and extending transversely of the electron path, opposite walls at one end thereof having apertures therethrough, said spaced electrodes registering with said apertures and connected to the walls of said resonator, said resonator being of substantially uniform transverse dimension normal to said electron path and having a smaller transverse dimension parallel to the electron path at said apertures than other portions of said resonator.

15. In combination an electron discharge device having an elongated envelope and having a cathode at one end thereof for supplying electrons along a given path, and another electrode in said path at the other end toward which said electrons are directed? during operation. of said device, aipair of spacedxgridamembers positioned betweensaid cathode andsaid electrode and; lying in said path and having radiallydirected contacts. and. supports extending:- through the wall of said envelope, andlan. elongated cavity resonatorclosed at. both ends and having a redetermined resonant. frequency. and: extending transversely-of theelectronpath and being of. substantially uniform transverse: dimension normal to said. electronpathJa-nd having a. portion of restricted: transverse. dimension parallel to said path at oneend and? provided; at said restricted portionwith a pair of. oppositely disposed'apertures through: which. said electrondischarge. deviceextends, said contactsand supports of said spaced gridsbeing connected to opposite walls ofisaid resonator.

1.6; An. electron discharge device having a cathode for supplying electrons along: a given path and: an electrode in said path toward which said electrons are directed during operation or said device, and an elongated cavityresonatorclosed at both ends and having a predetermined resonant frequency and: positioned between said cathode and said electrode and through which the electron path is directed, said cavity resonator having at oneend thereof a plurality of spaced portions of constricted transverse dimension paralleltosaid path; said. electron pathbeing directed through said spacedconstricted' portions.

I7. In combination, anelectron. discharge device having an elongated envelope, a cathode at one end of the envelope for supplying'electrons along a. given path, an electrode in said path at including'an elongated hollow conductingmember. provided at one-end-with aplurality ofportions of constricted transverse dimension parallel to said path, saidconstricted portions having registering apertures through which saidelectron discharge device extends; thegrid contacts being. electrically connected to the walls of said constricted portions at said apertures.

18.. Anelectron discharge device havinga cathode for supplying electrons along a givenpath and an electrode in-said'path toward which said electrons are directed during operation of said device, and a cavity resonator positioned between said cathode and said electrode and having an enlarged portion and a curved portion of restricted transverse dimension, said restricted por tion being provided with oppositely disposed foraminous sections disposed in said path and through which the electrons may be directed toward said electrode during operation of said device, said restricted portion communicating with said enlarged portion.

19. An electron discharge device having an envelope containing a cathode for supplying electrons along a given path and an electrode in said path toward which said electrons are directed during operation of said device, and a first cavity resonator section positioned between said cathode and said electrode and comprising a curved portion of restricted transverse dimension, said restricted portion being provided with oppositely disposed foraminous sections disposed in said path and through which the electrons may be directed toward said electrode during operation of said device, and a second cavity resonator section having an enlarged portion having a transverse dimension larger than that of said restricted portion and. positioned externally of said envelope, said cavity resonator sections having openends communicating with eachother;

20. An electron discharge device having an envelope, a cathode within said envelope for supplying electronsalong a given path, and an. electrode in said path. toward which said? electrons are. directed during operation of' said device, a first cavity resonator section positioned within said envelope andibetween said cathode and said electrode, said first. resonator section being U- shaped and. provided'intermediate the ends of the U. with foraminous portions disposed in said path. and through which electrons are directed toward said: electrodes during: operation of said device, the end of one leg. of said U being closed andtthe other open, and a second cavity resonaztor section outside said envelope and having a larger transverse section than. that. of said U shapedsection and coupled with the open leg of being. U:-shaped and provided intermediate the ends of the Uv with foraminous portions disposed in said path and through which electrons are directed toward said electrode during operation of'saidr' device, the end of one leg of said U being closed'andthe other open, and a; second. cavity. resonator section outside said envelope and coupled with the open leg oftlle first resonator section within said envelope. to provide aresonator.

22. An electron discharge device having a cathode for supplying electrons along a given path. and an electrode in said path toward which said electrons are directed during operation of saidzdevice, and a cavity resonator closedat both ends and having a predetermined resonant frequency and positioned between said cathode-and said. electrode and havinga-folded portion ofrestricted transverse dimension through which said path lies and a portion communicating with said folded portion having a corresponding transverse dimension greater than said transverse dimension of the folded portion.

23. An electron discharge device having a cathode for supplying electrons along a given path and an electrode in said path toward which said electrons are directed during operation of said device, and a cavity resonator closed at both ends and having a predetermined resonant frequency and positioned between said cathode and said electrode and having a folded portion of restricted transverse dimension through which said path lies and a portion communicating with said folded portion having a transverse dimension greater than the transverse dimension of the folded portion, adjacent folds being spaced from each other a distance equal to the distance travelled by an electron during a half period of the operating frequency of said resonator.

'- W 24.- An electron discharge device having a cathode for supplying electrons along a given path and an electrode in said path toward which said electrons are directed during operation of said device, and a cavity resonator closed at both ends and having a predetermined resonant frequency and positioned between said cathode and said electrode and having a folded portion of restricted transverse dimension through which said path lies and a portion communicating with said folded portion having a transverse dimension greater than the transverse dimension of the folded portion, said folds being adjacent each other with no spacing between.

' 25. An' elongated resonator having at one end a portion of restricted transverse dimension,

a cathode for supplying electrons along a given path positioned within said restricted portion and surrounded by a conducting 'member forming part of the wall of said resonator and provided with a foraminous section in said path through which electrons may be directed during operation of said device, another part of said wall registering with the first mentioned part and provided with a foraminous section through which said 'beam path lies, and an electrode in said path toward which said electrons are directed after passing through said foraminous sections during operation of said device.

26. An electron discharge device having an envelope containing a cathode for supplying electrons along a given path, a cavity resonator section surrounding said cathode within said envelope, said resonator section having an inner conducting wall surrounding said cathode and pro- .vided with a first foraminous portion in said path through which electrons may be directed during operation of said device, said resonator section having an outer wall provided with a second foraminous portion through which said path lies, an electrode positioned in said path outside of said resonator section and toward which said electrons are directed during operation of said .device, said resonator section being open along a portion thereof, and a cavity resonator section outside said envelope and communicating with the section inside said envelope, the section outside of said envelope having a transverse dimension larger than the corresponding transverse dimension of the section within said envelope.

27. An electron discharge device having an envelope and containing a cathode, a cavity resonator surrounding said cathode and having an inner wall surrounding said cathode, said inner wall being provided with a pair of' oppositely disposed foraminous portions, said resonator having an outer wall enlarged adjacent said cathode and provided with a pair of foraminous portions registering with the cathode and the foraminous portions of said inner wall, and a pair of electrodes on the outside of said resonator and registering with said foraminous portions and toward which electrons from said cathode are directed during operation of said device, said resonator being open along one portion thereof, and a cavity resonator externalof said envelope and having a portion telescoped over said envelope and over the open portion of said resonator within said envolep whereby the interior of the inner and outer resonators electrically communicate with each other, the resonator external of said envelope having a portion of transverse dimension greater than the corresponding dimension of the resonator within said envelope.

28. An electron discharge device having a cathode for supplying electrons along a given path and an electrode in said path toward which said electrons are directed during operation of said device, and an elongated cavity resonator closed at both ends and having a predetermined resonant frequency, the transverse dimensions of said resonator being uniform throughout the length thereof, one end of said resonator being divided into a plurality of spaced portions of small thickness compared to said transverse dimensions opening into the remainder of said resonator, said beam path extending through said spaced portions.

ERNEST G. LINDER.

REFERENCES CITED The following references are of record in the file of this patent:

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